The objectives of the study were to find out (a) the construct validity of the pupils' self-concepts in the last class of a primary school in Nigeria, and (b) the differences if any, between the sexes in their academic attainments. For the construct validity the self-description questionnaire (SDQ) of Mash, Farmer and Smith (I983) was used for the study. The teacher ratings were also obtained on a 9-Point scale for the purpose. Besides, the investigator obtained the pupils' school marks in mathematics, English and social studies and also obtained the overall mean of the school marks from their previous examination. The self descriotion questionnaire (SDO) consisted of seven categories such as, physical abilities, physical appearance, relationship with peers, relationship the parents, reading, mathematics and school subjects. The mean of the first four categories (physical abilities, physical appearance, relationship with peers, relationship with parents) formed their non-academic self concept (NACD), while the mean of the last three (reading, mathematics, English) formed their academic self-concept, while the mean of the seven categories gave their total self concept (TOT). To obtain the teacher ratings the teachers were instructed by the investigator on how to rate. The teachers gave their ratings on a 9-point scale on all these categories. From the teacher ratings as well, the investigator obtained the NACD, ACD and TOT scores, which were subjected to computer data analysis. The analysis of data revealed the construct validity to be ,039 (pupils' TOT with the Teachers' TOT), .091 (pupils' TOT with M3), and also .275 (Teachers' TOT with M3). It was however found that there were some differences for the girls' NACD concept and their school attainments. Comments on these differences have been discussed and the thesis ends with some discussion of the importance of SJQ which are highlighted,